1. Field of the Invention
This invention relates generally to a downhole drilling motor and bit assembly for use in rapidly changing the inclination of a borehole, and particularly to an articulated assembly that is adapted to drill a curved well bore section having a relatively short radius of curvature.
2. Description of the Related Art
When curved well bores are drilled with conventional techniques and equipment, a relatively long radius of curvature in the range of several hundred feet or more is required. Thus the overall length of the curved section is quite long and must be carefully monitored to ensure that the outer end of the section arrives at a specified location. Such equipment typically includes a mud motor having a bend angle built into its housing above the bit bearing section but below the power section of the motor. An undergage stabilizer usually is run above the bit to generally center it in the borehole while allowing it to drill a hole that curves gradually upward as the inclination angle builds up. The radius of curvature is controlled primarily by the bend angle being used, which typically can be in the range of from 1.degree.-3.degree.. However, even when a bend angle on the upper end of this range is employed, the radius of curvature still is rather long.
There are numerous circumstances where the drilling of a curved well bore section having a relatively short radius of curvature is advantageous. One example is where a vertical well bore is turned to the horizontal through vertical fractures in order to increase production. Also, the geology above the production zone may make it desirable to drill vertically through a certain rock layer and then curve the borehole sharply below it. Moreover, a relatively short radius of curvature allows the surface facilities to be closer to a position generally over the production zone than if a long radius curved section is drilled. It may also be desirable to drill several horizontal boreholes at different azimuths from a single vertical borehole to improve drainage. When a number of wells are drilled from an offshore platform, one or more wells having a horizontal section may be necessary to tap the production directly below the site of the platform. Other occasions where a horizontal well bore is needed will be apparent to those familiar with the art. In each case a short radius curve can be drilled in less time with reduced cost.
An object of the present invention is to provide a new and improved drilling motor assembly that is constructed and arranged to drill a curved borehole on a relatively short radius of curvature.
Another object of the present invention is to provide a new and improved articulated drilling motor assembly which allows the drilling of a curved borehole section having a short radius of curvature.
Still another object of the present invention is to provide a new and improved articulated drilling motor assembly which includes spaced stabilizer means having a bend angle therebetween to allow the inclination angle to build up at a high rate during drilling.